As is generally well known in the railway industry, truck mounted braking systems comprise, in addition to the brake beams, a series of force transmitting members, levers and linkages which function to move a group of brake shoes against the wheels of a railway vehicle to effect stoppage of such railway vehicle. These force-transmitting levers are pivotally-connected to each brake beam at its midpoint, with the corresponding lever arms of these force-transfer levers being connected to the force-transmitting members.
One of the force-transmitting members includes a slack adjuster device, the other force-transmitting member includes a pneumatically actuated brake cylinder device, the body of which is mounted on one brake beam between the beam tension and compression members adjacent the strut bar, and a connecting rod between the transfer lever arm of the other brake beam and the cylinder body. The brake cylinder piston push rod is connected to the transfer lever arm of one of the brake beams. Such cylinder initiates movement of this series of force transmitting members, levers and linkages to apply the brakes of the railway vehicle mounted to a truck assembly of such railway vehicle. A well known type of truck mounted braking system is a TMX.RTM. truck mounted braking system (TMX.RTM. is a registered trademark of Westinghouse Airbrake Company, the assignee of the present invention).
The TMX was designed for the standard North American three-piece railway truck application. In this application the axle movement is limited to the gaps between the axle bearings, bearing adapters and the side frame opening. Thus, the total gap or axle movement is substantially limited and in most cases does not exceed 0.187 of an inch. Because of this limited axle movement the required brake shoe clearance is maintained allowing the TMX system to work as intended.
In addition to the standard North American three-piece railway truck design, an Axle Motion III application having a swing motion bolster design have been used to improve railway vehicle performance on a curved track as railway vehicle truck members negotiate such curved track. In Axle Motion III applications the axle centerline is allowed to move approximately ±0.75 of an inch off a nominal centerline of the axles as the truck negotiates a curve. The allowed axle movement requires a greater brake shoe clearance to eliminate brake shoe drag against the truck wheel surface. Such brake shoe drag is a non-desirable condition as it facilitates unequal wheel wear and accelerated brake shoe wear.
As it can be seen from the above discussion it is desirable to improve TMX.RTM braking system performance to allow for additional brake shoe clearance.